1. Field of the Invention
The present invention relates to a damper device, a high pressure pump having the damper device and a manufacturing method of the high pressure pump.
2. Description of Related Art
For example, Japanese Unexamined Patent publication No. 2005-42554A (corresponding to US 2005/0019188A1) teaches a high pressure pump that includes a damper device, which damps, i.e., reduces pressure pulsation of fuel generated through reciprocating movement of a plunger.
In this damper device, two metal diaphragms are joined together to form a damper member, which is placed in a fluid chamber of the high pressure pump. Gas is filled in a damper chamber of the damper member. A pressure of the gas, which is filled in the damper chamber, is equal to or higher than the atmospheric pressure. Each diaphragm is configured into a dish form and includes a generally circular region and an outer peripheral region. The generally circular region serves as a movable portion, and the outer peripheral region is located radially outward of the generally circular region and serves as a non-movable portion. When the pressure of the fuel in the fluid chamber is changed, the movable portions of these two diaphragms are displaced relative to each other, thereby resulting in a change in the volume of the damper chamber of the damper member. In this way, the damper member implements the pressure pulsation damping effect (reducing effect) for damping the pressure pulsation of the fuel in the fluid chamber.
For instance, when the engine of the vehicle, which has the high pressure pump discussed above, is stopped, the pressure of the fluid chamber, in which the damper member is placed, becomes generally equal to the atmospheric pressure (this state of the fluid chamber will be hereinafter referred to as a non-operating state). Therefore, at this time, the damper member is bulged, so that the movable portions of the two diaphragms are bulged away from each other, i.e., are displaced away from each other in a separating direction. In this state, the stress is generated at or around the boundary between each movable portion and its adjacent non-movable portion in the damper member. Thereafter, when the operation of the high pressure pump is started, the pressure of the fuel in the fluid chamber is increased. This state of the fluid chamber at the time of starting the operation of the high pressure pump will be hereinafter referred to as an operation start time state. At this time, the movable portions of the two diaphragms are displaced toward each other in an approaching direction, and thereby the volume of the damper chamber is reduced. During the operation of the high pressure pump, the pressure of the fuel in the fluid chamber is repeatedly changed, i.e., is repeatedly decreased and then increased. The state of the fluid chamber during the operation of the high pressure pump will be hereinafter referred to as an operating state. When the movable portions of the two diaphragms are repeatedly moved toward each other and then moved away from each other in response to the repeated change of the pressure of the fuel in the fluid chamber, the volume of the damper chamber is repeatedly decreased and then increased.
When the state of the fluid chamber is changed from the non-operating state to the operation start time state or is in the operating state, the movable portions of the diaphragms of the damper member are displaced. Therefore, the stress, which is generated in the damper member, is also changed. The amount of displacement of the movable portions of the diaphragms at the time of changing from the non-operating state to the operation start time state is larger than the amount of displacement of the movable portions of the diaphragms in the operating state. Therefore, the amount of each displacement of the movable portions of the diaphragms as well as the number of times of displacement of the movable portions of the diaphragms at the time of changing from the non-operating state to the operation start time state have large influences on the lifetime of the damper member.
For instance, nowadays, the engine idling of the vehicle is temporarily stopped at, for example, the red traffic light for the purpose of improving the fuel consumption. In such a case, the number of times of change from the non-operating state to the operation start time is increased. Furthermore, the supply pressure of the fuel, which is supplied to the high pressure pump at the time of the engine start, is increased to improve the starting performance of the engine. In such a case, the amount of displacement of the movable portions of the diaphragms becomes large at the time of changing the state of the fluid chamber from the non-operating state to the operation start time state. Under such a condition, the lifetime of the damper member may be particularly reduced. It is conceivable to use a material, which exhibits a high fatigue strength, as the material of the diaphragms in order to lengthen the lifetime of the damper member. However, when the material, which exhibits the high fatigue strength, is used as the material of the diaphragms, the manufacturing costs of the damper device may be disadvantageously increased.